The long term goal of this study is to understand at the cellular level the effects of mechanical and electrical stimuli on bone growth and remodeling. The major objective for this project period are: (i) to characterize the cellular specificity of the responsive "state", with respect to cell type, state of differentiation, and cell-cycle stage and (ii) to study the mechanism for transduction of mechanical and electrical stimuli. The working hypothesis is that: (a) mild mechanical and electrical perturbations act selectively on skeletal cells; (b) the effect is target cell specific and depends on cellcycle stage and state of maturation; (c) accordingly, stimuli modulate proliferation or the expression of the differentiated phenotype; (d) the effects are influenced by other epigenetic factors; ions, hormones, etc.; (e) stimuli are transduced at the cell membrane by "second messenger" type mechanisms. The two stimuli to be tested are the clinically used pulsating electromagnetic fields and a hydrostatic intermittent compression of physiological magnitude. The perturbations will be applied to cells isolated from rat calvaria and to clonal cell lines from rat osteosarcoma, as well as subpopulations of the above, obtained by fluorescent activated cell sorting, using phenotypic surface markers. Effects will be evaluated by monitoring: a) Cell growth (cell number; 3HTdr/DNA specific activity; autoradiography; and cellcycle analysis by cytofluorometry). b) Ornithine decarboxylase activity, to estimate trophic stimulation on a short time scale. c) Alkaline phosphatase (chemically; histochemically; and by following cytofluorometrically the distribution of cells tagged with alkalinephosphatase antibodies), to evaluate effects on osteoblast-phenotypic expression. Other factors which affect above parameters will be tested in conjuction with mechanical and electrical stimuli: corticosteriods, prostaglandins and PTH. Signal transduction will be studied by searching for early biochemical changes (cAMP, 86Rb+ fluxes and by the use of inhibitors: (amiloride, ouabain, verapamil). The knowledge generated by this study should contribute to the efficient utilization of mechanical and electrical stimuli in the treatment of hard tissue problems, including craniofacial anamolies, bone loss in periodontal disease, bone fractures, and related disorders.